For example, a resolver used in a motor control system of a driving system of an automobile is required to have redundancy. FIG. 1 illustrates the configuration which is disclosed in Japanese Registered Patent No. 4157930 (Japanese Patent Application Laid Open No. 2000-18968) as a prior art example of this type of resolver. In FIG. 1, 11 denotes a stator, 12 denotes a first redundant resolver coil, 13 denotes a second redundant resolver coil, and 14 denotes a rotor.
In this example, first redundant resolver coils 12 and second redundant resolver coils 13 are provided to one stator 11 in a manner to be separated for every 90 degrees. A pair of first redundant resolver coils 12 is disposed on positions opposed to each other by 180 degrees and a pair of second redundant resolver coils 13 is disposed on positions opposed to each other by 180 degrees as well. Thus, the coils of two systems are provided to one stator 11 so as to provide redundancy, in this example.
Meanwhile, FIG. 2 illustrates the configuration of a rotation angle detecting device disclosed in Japanese Patent Application Laid Open No. 2008-216142. This rotation angle detecting device includes a rotation angle detecting unit 20, a signal processing unit 30, and wire harnesses 41 to 46 which are signal lines between the rotation angle detecting unit 20 and the signal processing unit 30.
The rotation angle detecting unit 20 includes two resolvers 21 and 22, and redundancy can be secured by arranging the two resolvers 21 and 22 concentrically on the same axis, for example. The resolvers 21 and 22 are variable reluctance resolvers. The resolver 21 is provided with an excitation coil 23 and detection coils 24 and 25, and the resolver 22 is provided with an excitation coil 26 and detection coils 27 and 28. Thus, the resolvers 21 and 22 are one-phase excitation and two-phase output resolvers. In this example, the detection coil 24 and the detection coil 27 forming a sin phase of the two resolvers 21 and 22 are connected in series and the detection coil 25 and the detection coil 28 forming a cos phase are also connected in series.
The signal processing unit 30 includes AC sources 31 and 32 which are respectively connected to the excitation coils 23 and 26 via the wire harnesses 41 and 46, a detector circuit 33 which detects detection signals of the resolvers 21 and 22 via the wire harnesses 42 to 45, and R/D converters 34 and 35 to which an output signal of the detector circuit 33 is inputted. The AC sources 31 and 32 respectively supply excitation signals of which frequencies are different from each other to the excitation coils 23 and 26.
A detection signal of a first frequency is induced in the detection coils 24 and 25 of the resolver 21, and a detection signal of a second frequency is induced in the detection coils 27 and 28 of the resolver 22. Since the detection coil 24 and the detection coil 27 are connected in series, a first multiplexed signal which is obtained by multiplexing a sin-phase detection signal of the first frequency which is induced in the detection coil 24 and a sin-phase detection signal of the second frequency which is induced in the detection coil 27 is inputted into the detector circuit 33. Further, a second multiplexed signal which is obtained by multiplexing a cos-phase detection signal of the first frequency which is induced in the detection coil 25 and a cos-phase detection signal of the second frequency which is induced in the detection coil 28 is inputted into the detector circuit 33.
The detector circuit 33 separates these inputted first and second multiplexed signals into a detection signal of the first frequency and a detection signal of the second frequency. To the R/D converters 34 and 35, the signals separated by the detector circuit 33 are inputted. The R/D converter 34 calculates a rotation angle θ1 which is detected by the resolver 21, based on a sin-phase output signal and a cos-phase output signal of the first frequency, and in a similar manner, the R/D converter 35 calculates a rotation angle θ2 which is detected by the resolver 22, based on a sin-phase output signal and a cos-phase output signal of the second frequency. In a case where the resolvers 21 and 22 are disposed adjacent to each other on the same rotation axis, these rotation angles θ1 and θ2 are equal to each other, being able to secure redundancy.
Here, in the resolver illustrated in FIG. 1, the first redundant resolver coil 12 and the second redundant resolver coil 13 are separately provided. Accordingly, when a one-phase excitation and two-phase output resolver is employed, for example, an excitation coil and two detection coils are required for each of the first redundant resolver coil 12 and the second redundant resolver coil 13. Therefore, the number of wirings for the resolvers is 12 in total and thus the wiring is complicated disadvantageously.
On the other hand, in the configuration illustrated in FIG. 2, redundancy can be secured by disposing the two resolvers 21 and 22 on the same rotation axis. Detection signals can be multiplexed by changing frequencies of excitation signals of the two resolvers 21 and 22 and thus increase of the number of wirings (the number of wire harnesses) can be suppressed.
However, the configuration illustrated in FIG. 2 requires two pieces of resolvers 21 and 22. Further, redundancy is secured only when abnormality such as disconnection occurs on an excitation coil of one of the resolvers, but a rotation angle cannot be detected when abnormality such as disconnection occurs on any one of detection coils, deteriorating redundancy.